With increasing demand for liquid transportation fuels, decreasing reserves of ‘easy oil’ (crude petroleum oil that can be accessed and recovered easily) and increasing constraints on the carbon footprints of such fuels, it is becoming increasingly important to develop routes to produce liquid transportation fuels from alternative sources in an efficient manner.
Biomass offers a source of renewable carbon and refers to biological material derived from living or recently deceased organisms and includes lignocellulosic materials (e.g., wood), aquatic materials (e.g., algae, aquatic plants, and seaweed) and animal by-products and wastes (e.g., offal, fats, and sewage sludge). Liquid transportation fuels produced from biomass are sometimes referred to as biofuels. Therefore, when using such biofuels, it may be possible to achieve more sustainable CO2 emissions over petroleum-derived fuels.
However, in the conventional pyrolysis of biomass, typically fast pyrolysis carried out in an inert atmosphere, a dense, acidic, reactive liquid bio-oil product is obtained, which contains water, oils and char formed during the process. The use of bio-oils produced via conventional pyrolysis is, therefore, subject to several drawbacks. These include increased chemical reactivity, water miscibility, high oxygen content and low heating value of the product. Often these products are difficult to upgrade to fungible liquid hydrocarbon fuels.
An efficient method for processing biomass into high quality liquid fuels is described in WO2010117437, in the name of Gas Technology Institute. The method described in WO2010117437 for the conversion of biomass into liquid hydrocarbon fuels uses catalytic hydropyrolysis and hydroconversion steps. While not being limited to any particular catalyst, exemplary catalysts for use in such processes include sulfided catalysts containing nickel, molybdenum, cobalt or mixtures thereof as active metal(s).
Biomass-containing or biomass-derived feedstocks, such as feedstocks containing municipal solid waste, waste plastics, food waste and feedstocks containing lignocellulose (e.g. woody biomass, agricultural residues, forestry residues, residues from the wood products and pulp & paper industries) are important feedstocks for biomass to fuel processes due to their availability on a large scale. Some of these materials, in particular municipal solid waste containing waste paper, cardboard, polyvinyl chloride plastic or food waste, and agricultural residues such as corn stover, rice husk, marine and brackish water plants or microorganisms such as marine microalgae or macroalgae contain high levels of impurities, such as chlorides, which can have a detrimental effect on the overall process.
Chlorides contained within biomass-containing or biomass-derived feedstocks may be liberated during a high temperature hydropyrolysis step (for example at temperatures in excess of 400° C.). Liberated chlorides may also react with any hydrogen present to produce vapour-phase hydrogen chloride.
The presence of vapour phase chlorides may cause corrosion in the reactor and other process equipment. Process equipment containing aqueous phase product is particularly susceptible to corrosion, as chlorides may preferentially dissolve in water and contribute to corrosion of the heat exchangers, gas-liquid separators, and other process equipment handling the aqueous phase. Further, hydrogen chloride dissolves in water to produce a low-pH aqueous phase containing hydrochloric acid. Typical materials used for process equipment in high-temperature hydrogen-handling services, such as austenitic stainless steels, are highly susceptible to chloride attack.
Vapour-phase chlorides may also act as poisons for catalysts used in hydropyrolysis and hydroconversion processes, deactivating the catalysts and reducing the overall efficiency of such a process. Hydrogen sulfide (H2S) sorbents, such as zinc oxide-based sorbents may also be negatively affected by the presence of chlorides in a reaction system.
The presence of chlorides in the process gas is a commonly encountered problem in a number of industries. The strategies used for mitigation of the effects of chloride in the process stream often rely on the use of a chloride trap used as a sorbent in the form of pellets for a fixed bed reactor, or granules for a fluidized bed reactor. The use of calcium and sodium-based sorbents to capture chlorine in the pyrolysis of municipal waste is described in Fontana, A., et al., 1999, Erdöl-Erdgas-Kohle, Nr 2001, p 117.
Another challenge in processing certain types of material such as waste paper and packaging waste by hydropyrolysis in a fluidised bed reactor is the poor flow properties of these materials. This may be attributed to the high aspect ratio of paper and cardboard, that is, the very high ratio of the lateral dimension of a piece of shredded paper or cardboard to the thickness of paper or cardboard. The flat and elongated pieces obtained by shredding paper or cardboard are found to stack on top of each other, and flow poorly or don't flow at all, when dosing is attempted using a screw dosing system. Sorted municipal solid waste comprising of waste paper, cardboard and plastics that is simply shredded is also ‘fluffy’ and has a low-density, causing further transportation and processing issues. The present inventors have found, therefore, that densification of the feedstock and processing to improve the aspect ratio of the feedstock is a necessary step for conversion of certain municipal solid waste in a catalytic hydropyrolysis reactor.
It would be advantageous to develop an effective process to convert chloride-containing biomass, particularly waste products such as waste paper, plastics and cardboard, into useful liquid hydrocarbon materials while mitigating the problems, such as corrosion and catalyst poisoning, associated with chlorides present in such biomass. Overcoming handling and dosing issues associated with certain biomass sources would also be advantageous.